296 
Maugham— On the Mechanism of 
It is clear then, that if changes occur in the concentration of solutes 
present in a heterogeneous system containing one or more constituents capable 
of adsorbing them, there will be a succession of readjustments of equilibrium 
between the concentration of the solute at the surface of the adsorbing 
phase and that of the solute in the solvent. 
Such changes may be brought about in plant cells owing to variations 
in the supply of both water and of solutes. Thus there would result a state 
of continuous flux, the solute constantly varying in concentration in the two 
regions. 
It should be realized that the conception here outlined does not imply 
Fig. 1. FB, Type of curve showing reversible adsorption equilibria with a given solute, 
solvent, and adsorbing phase B. The broken lines represent equilibria with other adsorbing 
phases A, c, and d, in which the solute is assumed to undergo different degrees of adsorption 
indicated by E 1, E 3, and E4. 
that particular molecules of sugar are, as it were, fixed on the surface of the 
adsorbing phase, while others are free to move in the solvent, but rather that 
molecules are at all times passing from the surface of the adsorbing phase 
into the body of the solvent, and vice versa, in such a manner that a definite 
relation between their concentrations in the two regions is maintained while 
the conditions are constant. 
There is therefore the possibility that an individual molecule might 
remain for a very long period in, say, a bundle-sheath cell, if it managed to 
confine its peregrinations to the more central parts of the vacuole well out 
of immediate reach of the protoplasm. Obviously the layer of solution 
actually bathing the adsorbing substance will be the site of initial re- 
